Actuator with two motors, a differential reducer and a torque limiter

ABSTRACT

The invention relates to an actuator comprising two drive motors ( 14 A,  14 B), an outlet ( 22 ), a differential reducer ( 16 ) with spur teeth and a torque limiter ( 18 ), the latter two components being disposed between the two motors ( 14 A,  14 B) and the outlet ( 22 ). According to the invention, the torque limiter ( 18 ) is built into the differential reducer ( 16 ). The invention can be used to anchor a landing gear.

The present invention relates to an actuator of the type comprising:

-   -   two drive motors,    -   an output member,    -   a differential reduction gear having straight-cut teeth which is        interposed between the two motors and the output member, the        differential reduction gear comprising:        -   two sun pinions, each sun pinion being rotatably coupled to            a drive motor,        -   an output shaft, about which the axes of the sun pinions are            rotatably mounted,        -   a planet-carrying drum which is connected to the output            shaft in order to be rotatably driven,        -   at least one pair of planet pinions which are carried by the            planet-carrying drum and which are mounted so as to rotate            about themselves, each planet pinion being engaged with a            sun pinion, the associated planet pinions of the same pair            being engaged with each other,    -   a torque limiter which is interposed between the two motors and        the output member.

Such an actuator is used in particular for locking the undercarriage ofan aircraft in a retracted position.

For reasons of reliability, the actuator comprises two motors fordriving the output member. A differential reduction gear is arrangedtherebetween and allows the output member to be driven by the two motorswhen they operate, even if the speeds thereof are different. Owing tothe differential reduction gear, the output member is driven by only oneof the motors, should the other motor break down.

In order to prevent any risk of damage to the mechanism of theundercarriage, a torque limiter is provided in the actuator.

Basically, the torque limiter is a differential reduction gear.

The presence in the same actuator of two drive motors, a differentialreduction gear and a torque limiter results in the actuator taking up alarge amount of space.

The object of the invention is to provide an actuator provided with twomotors, a differential reduction gear and a torque limiter which takesup less space.

To this end, the invention relates to an actuator of the above-mentionedtype, characterised in that the torque limiter brings about theconnection between the planet-carrying drum and the output shaft, whichtorque limiter is arranged between the two sun pinions on the axis ofthe output shaft.

According to specific embodiments, the actuator further comprises one ormore of the following features:

-   -   the torque limiter comprises friction members, which are fixedly        joined in terms of rotation to the output shaft and the        planet-carrying drum, and means for clamping the friction        members against each other;    -   the friction members have annular planar friction surfaces and        the clamping means are suitable for applying a force for        clamping the surfaces against each other in the direction of the        output shaft;    -   the output shaft has an axial support and a threaded portion, on        which a nut is screwed, and the friction members are engaged        around the output shaft and are held clamped between the axial        support and the nut;    -   at least one of the axial support and the nut is arranged        outside the space defined between the two sun pinions and it        comprises a spacer which is engaged around the shaft and which        brings about the support of a friction member on at least one of        the axial support and the nut and at least one sun pinion is        mounted for rotation about that spacer;    -   the or each friction member which is fixedly joined in terms of        rotation to the planet-carrying drum comprises a hub having        radial projections for being fixedly joined to the planet        carrier, delimiting between them openings for receiving the        associated planet pinions of the same pair; and    -   the torque limiter comprises a single friction member which is        fixedly joined in terms of rotation to the planet-carrying drum        which is clamped between two friction members which are fixedly        joined to the output shaft.

The invention will be better understood from a reading of thedescription below given purely by way of example and with reference tothe drawings, in which

FIG. 1 is a partially cut away perspective view of an actuator accordingto the invention;

FIG. 2 is a longitudinal section of the actuator of FIG. 1;

FIG. 3 is a partially cut away perspective view of the differentialreduction gear and torque limiting mechanism of the actuator of FIGS. 1and 2;

FIG. 4 is an exploded perspective view of the mechanism of FIG. 3; and

FIG. 5 is a longitudinal section of the mechanism illustrated in FIGS. 3and 4.

The actuator 10 illustrated in the Figures is intended for locking anaircraft undercarriage in a retracted position.

That actuator comprises a housing 12, inside which two drive motors 14A,14B are arranged, each connected mechanically to a differentialreduction gear and torque limiting mechanism 15. That mechanismcomprises a differential reduction gear 16 which includes a torquelimiter 18. The actuator further comprises an epicyclic reduction gear20 which is driven by the mechanism 15 and a rotating output member 22which protrudes from the housing 12 and which is itself driven by theepicyclic reduction gear 20.

In greater detail, the two motors 14A, 14B are constituted by electricmotors, whose stators 24A, 24B are fixedly joined to the housing 12 andwhose rotors 26A, 26B can rotate about axes Y1—Y1 and Y2—Y2 which extendparallel with each other.

The output shafts 28A, 28B of the motors drive the first and secondmotor sun pinions 30A, 30B of the differential reduction gear 16. Thosemotor sun pinions can rotate around the same principal axis X—X whichextends parallel with axes Y1—Y1 and Y2—Y2 of the motors.

As illustrated in FIG. 2, the output shaft 28A of the motor is coupledto the motor sun pinion 30A in order to be caused to rotate by areduction step 32A which is constituted by two coaxial and fixedlyjoined pinions 34A, 36A having different diameters.

Similarly, as illustrated in FIG. 1, the output shaft 28B of the motoris coupled in terms of rotation to the motor sun pinion 30B by areduction step 32B which is constituted by two coaxial pinions whichhave different diameters 34B, 36B and which are fixedly joined by ashaft 38.

The speed differential reduction gear and torque limiting mechanism 15is illustrated alone in FIGS. 3 to 5. It has an output shaft 40 whichextends along axis X—X. That shaft has, at a first end, an output pinion42 which can drive the epicyclic reduction gear 20.

The two motor sun pinions 30A, 30B are mounted so as to rotate freelyabout the output shaft 40. The axes of the pinions 30A, 30B and theoutput shaft 40 are identical. The pinions 30A, 30B are supported bythat shaft and are guided in rotation about the shaft by slidingbearings or rolling bearings 44A, 46A and 44B, 46B having lateralshoulders for axial retention.

Clamping jaws 48A, 48B are arranged between those bearings and the shaft40. Those jaws are constituted by sleeves 50A, 50B which are extended atthe facing ends thereof by integral collars 52A, 52B. The jaws 48A, 48Bare connected in terms of rotation to the shaft 40, but are free toslide in translation along the length thereof. For this purpose,complementary profiles, such as flat portions, are provided on the outersurface of the shaft 40 and on the inner surface of the jaws 48A, 48B.

The differential reduction gear 16 comprises, between the two motor sunpinions 30A, 30B, a planet carrier 60 which is constituted by twoend-plates 62A, 62B which are fixedly joined to each other in terms ofrotation by pins and screws 63. Between the two end-plates 62A, 62B ofthe planet carrier there are mounted pairs of planet pinions 64A, 64Bwhich engage with each other and each of which engages with a smalldriving sun pinion 70A, 70B which is fixedly joined to the motor sunpinion 30A and 30B, respectively.

Each planet pinion is in fact formed by two identical coaxial andintegral gears which are carried by a shaft 72, with which they areintegral.

The shafts 72 can rotate about themselves relative to the end-plates62A, 62B, between which they are held by means of bearings 74. Theshafts 72 extend parallel with each other and parallel with axis X—X ofthe output shaft 40. The axes of the shafts 72 are different from axisX—X so that the planet pinions 64A, 64B can rotate together as anassembly about axis X—X.

A hub 80 is fixedly joined in terms of rotation to the planet carrier 60by the pins 63. This hub is mounted so as to be able to rotate about theshaft 40. It is arranged between the two motor sun pinions 30A, 30B. Thehub 80 is more clearly visible in FIG. 4. It is of planar form with agenerally annular core which is extended by two diametrically opposedlateral lugs, through which the pins 33 extend. The pinions 64A, 64B arearranged around the core in the openings provided between the laterallugs.

The hub 80 comprises two friction discs 82A, 82B which are attached bymeans of adhesive bonding at the opposing planar surfaces thereof. Theyare held compressed between the collars 52A, 52B of the jaws 48A, 48B,those collars forming friction members which can co-operate with thefriction discs over planar annular surfaces.

The output shaft 40 is supported by ball bearings 90A, 90B which arearranged at one side and the other of the mechanism 15. Those ballbearings are supported by the housing 12. The shaft 40 has a collar 92which can be supported axially on the ball bearing 90 which is supportedaxially on a shoulder of the housing 12.

The hub 80 is clamped axially between the two jaws 48A, 48B. The jaw 48Bis supported on the collar 92 by means of a stack of Belleville washers94B and a rigid washer 96B.

The jaw 48A is pressed by a rigid washer 96A and a stack of Bellevillewashers 94A. That stack carried by the shaft 40 is held clamped by meansof a nut 100 which is screwed and centred on the second end of the shaft40 opposite that which presses against the pinion 42. The ball bearing90A is engaged around that nut 100 over a length of the nut having asmooth surface at the outer side.

In that manner, the nut 100 brings about axial retention of the hub 80which is clamped between the two jaws 48A, 48B. Those jaws 48A, 48B areurged towards each other by the Belleville washers 94A, 94B by means ofthe support washers 96A, 96B. The Belleville washers are held compressedat one side by the collar 92 and, at the other side, by the nut 100.

Depending on the tightening of the nut 100, the Belleville washers arecompressed to a greater or lesser extent and the pressure which theyapply to the jaws 48A, 48B can be adjusted in such a manner that thefriction force between the jaws 48A, 48B and the friction discs 82A, 82Bis modified.

In order to adjust the friction force, the housing 12 has an opening 110which is provided in the extension of the output shaft 40 and whichallows access to the nut 100 and allows it to be operated with aspanner. In order to bring about the securing of the nut, the shaft 40has, at the second end thereof carrying the nut, transverse recesses 112which open at the end of the shaft. There are, for example, threerecesses. Corresponding recesses 112, 114 are provided in the nut 110.They also open at the end of the nut.

A locking member 120 which is constituted by a collar 122 which carriestwo locking fingers 124 is engaged at the end of the shaft in such amanner that the fingers are received in corresponding radial recesseswhich are provided at the end of the shaft 40 and in the nut 100.

A screw 126 is engaged in a threaded hole 128 which is provided axiallyat the end of the shaft. It extends through the locking member 120 andbrings about its retention.

The opening 110 is closed by a removable and leak-tight protection plug140.

The actuator operates as follows.

When the two motors rotate at the same speed, the two motor sun pinions30A, 30B are driven in the same direction. In that manner, theassociated planet pinions 64A, 64B of the same pair are stationaryrelative to each other. The planet carrier 60 is caused to rotate by theplanet pinions which are themselves caused to rotate about shaft X—X bythe driving sun pinions 70A, 70B.

The hub 80 is then caused to rotate with the planet carrier 60.

The torque provided by the motors is transmitted from the hub 80 to theshaft 40, as long as the friction force applied between the clampingjaws 48A, 48B and the friction discs 82A, 82B is greater than the torqueprovided by the motors.

If that torque provided by the motor is greater than the friction forceapplied by friction, the friction discs slide over the friction surfacesof the jaws in such a manner that only a portion of the torque istransmitted. Therefore, the hub clamped between the clamping members48A, 48B forms a torque limiter which is interposed between the twomotor sun pinions 30A, 30B.

If one of the motors rotates at a different speed relative to the othermotor, or if one of the motors is stopped, the two driving sun pinions70A, 70B rotate at different speeds so that the planet pinions 64A, 64Bare caused to rotate about themselves in opposite directions,compensating for the difference in speed of rotation of the two motors.The planet carrier 60 is then driven at a mean speed between the speedsof the two motor sun pinions 30A, 30B, thus driving the shaft 40 at thatspeed as long as the torque provided by the motors is less than thefriction torque applied by the friction surfaces in contact.

As known per se, the shaft 40 drives the control member 22 by means ofthe epicyclic reduction gear 20.

Since the torque limiter is interposed between the two motor sun pinions30A, 30B, the space taken up by the reduction gear and torque limitingmechanism is reduced, which allows an actuator to be produced whichgenerally takes up little space.

In order to bring about the adjustment of the torque limiter, the plug110 is removed, thereby allowing access to the screw 126. The screw 126is removed, as well as the locking member 120. The nut 100 is screwed orunscrewed in order to bring about a suitable clamping force for the twojaws 48A, 48B on the friction discs 82A, 82B.

After the position of the nut has been adjusted, the locking member 120is re-engaged in corresponding recesses 114, 116 of the nut and the endof the shaft, and the screw 126 is re-tightened in order to bring aboutaxial retention of the locking member 120. Finally, the plug 140 isre-positioned in order to ensure the leak-tightness of the housing.

It will thus be appreciated that, in such an actuator, the torquelimiter can be calibrated after the actuator assembly has beenassembled, thereby allowing consideration to be given to friction andlosses of efficiency caused by the various engaged elements whichconstitute the actuator, and in particular the pinions of the epicyclicreduction gear 20. In that manner, the maximum output torque of theactuator measured at the output member 22 can be defined precisely,whatever the machining quality of the various moving elements of theactuator.

1. Actuator comprising: two drive motors (14A, 14B), an output member(22), a differential reduction gear (16) having straight-cut teeth whichis interposed between the two motors (14A, 14B) and the output member(22), the differential reduction gear (16) comprising: two sun pinions(30A, 70A, 30B, 70B), each sun pinion being rotatably coupled to a drivemotor (14A, 14B), an output shaft (40), about which the axes of the sunpinions (30A, 70A, 30B, 70B) are rotatably mounted, a planet-carryingdrum (60) which is connected to the output shaft (40) in order to berotatably driven, at least one pair of planet pinions (64A, 64B) whichare carried by the planet-carrying drum (60) and which are mounted so asto rotate about themselves, each planet pinion (64A, 64B) being engagedwith a sun pinion (30A, 70A, 30B, 70B), the associated planet pinions(64A, 64B) of the same pair being engaged with each other, a torquelimiter (18) which is interposed between the two motors (14A, 14B) andthe output member (22), characterised in that the torque limiter (18)brings about the connection between the planet-carrying drum (60) andthe output shaft (40), which torque limiter (18) is arranged between thetwo sun pinions (30A, 70A, 30B, 70B) on the axis of the output shaft(40).
 2. Actuator according to claim 1, characterised in that the torquelimiter (18) comprises friction members (80, 82A, 82B, 52A, 52B), whichare fixedly joined in terms of rotation to the output shaft (40) and theplanet-carrying drum (60), and means (92, 94A, 94B, 100) for clampingthe friction members (80, 82A, 82B, 52A, 52B) against each other. 3.Actuator according to claim 2, characterised in that the frictionmembers (82A, 82B, 52A, 52B) have annular planar friction surfaces, andin that the clamping means (92, 94A, 94B, 100) are suitable for applyinga force for clamping the surfaces against each other in the direction ofthe output shaft (40).
 4. Actuator according to claim 3, characterisedin that the output shaft (40) has an axial support (92) and a threadedportion, on which a nut (100) is screwed, and in that the frictionmembers (80, 82A, 82B, 52A, 52B) are engaged around the output shaft(40) and are held clamped between the axial support (92) and the nut(100).
 5. Actuator according to claim 4, characterised in that at leastone of the axial support (92) and the nut (100) is arranged outside thespace defined between the two sun pinions (30A, 70A, 30B, 70B), in thatit comprises a spacer (50A, 50B) which is engaged around the shaft andwhich brings about the support of a friction member (52A, 52B) on atleast one of the axial support (92) and the nut (100), and in that atleast one sun pinion (30A, 70A, 30B, 70B) is mounted for rotation aboutthat spacer (50A, 50B).
 6. Actuator according to claim 2, characterisedin that the or each friction member (82A, 82B) which is fixedly joinedin terms of rotation to the planet-carrying drum (60) comprises a hub(80) having radial projections for being fixedly joined to the planetcarrier (60), delimiting between them openings for receiving theassociated planet pinions of the same pair.
 7. Actuator according toclaim 3, characterised in that the torque limiter (18) comprises asingle friction member (82A, 82B) which is fixedly joined in terms ofrotation to the planet-carrying drum (60) which is clamped between twofriction members (52A, 52B) which are fixedly joined to the output shaft(40).
 8. Actuator according to claim 3, characterised in that the oreach friction member (82A, 82B) which is fixedly joined in terms ofrotation to the planet-carrying drum (60) comprises a hub (80) havingradial projections for being fixedly joined to the planet carrier (60),delimiting between them openings for receiving the associated planetpinions of the same pair.
 9. Actuator according to claim 4,characterised in that the or each friction member (82A, 82B) which isfixedly joined in terms of rotation to the planet-carrying drum (60)comprises a hub (80) having radial projections for being fixedly joinedto the planet carrier (60), delimiting between them openings forreceiving the associated planet pinions of the same pair.
 10. Actuatoraccording to claim 5, characterised in that the or each friction member(82A, 82B) which is fixedly joined in terms of rotation to theplanet-carrying drum (60) comprises a hub (80) having radial projectionsfor being fixedly joined to the planet carrier (60), delimiting betweenthem openings for receiving the associated planet pinions of the samepair.
 11. Actuator according to claim 4, characterised in that thetorque limiter (18) comprises a single friction member (82A, 82B) whichis fixedly joined in terms of rotation to the planet-carrying drum (60)which is clamped between two friction members (52A, 52B) which arefixedly joined to the output shaft (40).
 12. Actuator according to claim5, characterised in that the torque limiter (18) comprises a singlefriction member (82A, 82B) which is fixedly joined in terms of rotationto the planet-carrying drum (60) which is clamped between two frictionmembers (52A, 52B) which are fixedly joined to the output shaft (40).13. Actuator according to claim 6, characterised in that the torquelimiter (18) comprises a single friction member (82A, 82B) which isfixedly joined in terms of rotation to the planet-carrying drum (60)which is clamped between two friction members (52A, 52B) which arefixedly joined to the output shaft (40).